1. Field of the Invention
The present invention relates to a sine wave generation circuit for stepwisely changing a voltage level of an output in synchronization with an input clock signal and generating a pseudo sine wave.
2. Description of the Related Art
Generation of a sine wave signal is a very important in analog signal processing. There are various means for realizing this depending on the application and the required precision. The performance required for a circuit for generation of a sine wave signal is defined as the ability to generate a high precision sine waveform in synchronization with a reference digital clock signal. A “high precision waveform” means a waveform having an accurate phase, a low harmonic component, and an accurate signal amplitude with respect to the clock.
As the configuration of a sine wave generation circuit, a sine wave circuit of a so-called D/A conversion type for generating a pseudo sine wave by generating a binary-value pulse signal controlling the timing and changing an input resistance of an output amplifier by this is known (see for example Japanese Unexamined Patent Publication (Kokai) No. 5-183341 and Japanese Unexamined Patent Publication (Kokai) No. 10-209757).
In the technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-183341, switches are connected to nodes of a resistor series, and the on/off timings of the switches are controlled. The circuit for generating a binary-value signal for controlling the timing has a counter for counting the input clock signals, sequentially dividing each by ½, and outputting the same and a circuit for generating isolated pulse signals successively shifted by one clock pulse each by a logical operation of the divided signals.
The technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-209757 has a plurality of resistors connected in parallel between a constant current source and a ground potential and switches connected in series to the resistors and controls the on/off timings of these switches. The circuit for generating the binary-value signal for controlling the timing is basically the same as the one in the technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-183341 and has a frequency division circuit and an N-nary ring counter.
In a conventional sine wave generation circuit having such a configuration, however, when trying to generate a high precision pseudo sine wave such as one finely sampling a sine wave, the problems are encountered that the number of divisions of the frequency division circuit and the scale of the counter increase along with the number of samplings of the sine wave or the logical operation circuit for generating the isolated pulse signals becomes complex.
These problems are due to the fact that the conventional sine wave generation circuit generated all control signals for generating the coefficients (resistance values) determining the voltage value of the pseudo sine wave as binary-value pulse signals by digital signal processing.